This invention relates in general to ink ribbon-guide apparatus and more particularly to ink ribbon-guide apparatus employed in serial printers which employ ribbon cartridges.
The use of ribbon cartridges for typewriters and serial printers to assist in the installation of ribbons into such machines and to minimize the soiling of fingers during such process is well known in the art. In addition to minimizing typist contact with the ribbons, ribbon cartridges minimize and in certain cases eliminate the tedious threading of the ribbon through various ribbon guide and/or lift mechanisms. Also, the use of ribbon cartridges has been found helpful in increasing the useful life of the ribbons and the quality of printing by shielding the ribbon from exposure to the surrounding environment. But even with the use of ribbon cartridges, it is still often necessary to thread the ribbon through various ribbon guide and/or lift mechanisms. The type and layout of the ribbon guide and/or lift mechanism for a serial printer is determined by the particular printing environment. The ribbon cartridge provides, for use at the printing area or position, an unsupported length of ribbon from an axit port to an entrance port in the ribbon cartridge.
In regard to the guiding of ink ribbons across the printing area, it is well known to use a combination ribbon guide and ribbon lift in conjunction with a type-bar printer using separate ribbon supply and ribbon take-up spools as disclosed in U.S. Pat. Nos. 2,815,110 and 3,409,113. In this type of application, the unsupported span of ribbon between the outer sections of the ribbon guide is relatively short because of the narrow width of the type-bar printing element.
It is also known to use a combination ribbon guide and ribbon lift in conjunction with a ball-type printhead printer using a ribbon cartridge on a movable carriage as shown in U.S. Pat. Nos. 3,346,090 and 3,349,887. Although the unsupported span of ribbon is greater because of the ball-type printhead, the printhead normally rests a relatively large distance from the ribbon and approaches and contacts the ribbon only during the actual printing sequence.
It is also known to use a suction or vacuum in conjunction with the ribbon guide surface to hold the ribbon in close contact with the guide surface as disclosed in U.S. Pat. No. 2,973,082.
In U.S. Pat. No. 3,799,315, a ribbon guide is disclosed which is pivotally connected to and laterally extends from the ribbon cartridge to guide the ribbon from the ribbon cartridge to the print station and back to the ribbon cartridge.
The Diablo Corporation, a subsidiary of the present assignee, is marketing a serial printer under the tradename of Diablo Hytype I which employs a print wheel or disc-shaped type carrier. The Diablo Hytype I printer is enjoying commercial success as a serial printer in such applications as communication terminals, computer output devices, etc. The present assignee has recently marketed an electronic typing system for use in the office environment and used the Diablo Hytype I as the basis for the printer subsystem. The Diablo Hytype I provides superior performance for the particular market and environment for which it was designed. In using the Diablo Hytype I as the printer subsystem of the electronic typing system for use in the office environment, it was desirable to improve the print quality of the printed record. The Diablo Hytype I uses a ribbon cartridge containing a fabric ribbon. The quality of printing obtained from the fabric ribbon could be improved and a change was made to the matrix-type plastic ribbon from which a higher quality of printed material may be obtained. It was also necessary to greatly increase the hammer energy so the hammer would impart each character slug against the ribbon with a greater force. The necessary change in the hammer solenoid required to obtain the higher hammer energy necessitated a slight change in the mounting bracket for the ribbon guide of the Hytype I serial printer. The ribbon guide of the serial printer in the office environment must guide and control the ribbon precisely in order to maintain the high print quality demanded.
With reference to FIG. 1, the traditional vertical guide bars of the prior art Hytype I serial printers are approximately 2.25 inches apart; therefore, the ribbon is unsupported across the length of this span. In this environment, when the matrix-type plastic ribbon was impacted between the character slug of the print wheel and the paper, the plastic ribbon tended to curl or become cup-shaped around a longitudinal centerline of the ribbon. The upper and lower edges of the plastic ribbon curled toward the print wheel. The spacings between the paper, ribbon and print wheel are extremely close and on occasions the curled edge or edges of the plastic ribbon would make contact with the print wheel while the print wheel was rotating to the next print position. When this type of contact occurred, two basic types of malfunctions occurred: (1) the plastic ribbon was flipped to the backside of the print wheel resulting in a complete loss of printing or (2) the plastic ribbon was prevented from completely lifting to its print position from its lower rest position resulting in the loss of that particular character or the cropping of the upper portions of the characters.
With these prior art problems in mind, it is a primary object of the present invention to develop a ribbon guide suitable for a wide range of impact printing environments.
Another object of this invention is the construction of an economical method and apparatus for guiding ink ribbons for serial printers.
Yet, another object of this invention is to improve the guiding of ink ribbon fed between spools in a ribbon cartridge of the type used in serial printers.
A further object of this invention is the construction of a ribbon guide having improved mechanical and functional features over prior ribbon guides.
Other objects and advantages will be evident from the specification and claims and the accompanying drawing illustrative of the invention.